The purpose of this study is to quantitatively analyze CSF kinetics in multiple anatomical regions utilizing serialmetrizamide (Amipaque) enhanced CT images in three rhesus monkeys. A major goal of this project is the development of clinically useful and objective procedures for accurate diagnosis of cerebral atrophy versus normal pressure hydrocephalus. This approach will assist in the selection of patients who will likely profit by CFS diversionary shunt operation. During general anesthesia, each monkey will receive metrizamide (190 mg. I/cc), and have sequential CT scans using a whole-body CT scanner. Computer-assisted processing techniques will allow the definition of CT numbers in numerous anatomical regions which will lead to time-density curves for each region. Data processing will include mathematical modeling and the definition of quantitative parameters. Pilot studies have been performed in two monkeys.